It is generally known that dryers may be disposed at or between printing units as well as in the delivery area in order to support the drying and curing processes of printing inks and lacquers. This causes transfer of large amounts of heat from the UV or infrared dryers to the printing stock and the parts of the printing press adjacent to the dryers. Furthermore, printing with constant high speeds and with highly viscous (nonaqueous) printing inks further heats the cylinders guiding the printing ink and the sheets. The amount of heat transferred to the printing stock and printing press due to friction, convection or radiation is a significant interfering parameter in the printing process, because it changes the viscosity of the printing ink so that the ink control is affected and there is a greater danger that sheets will adhere or that thermally sensitive printing stock, such as plastic sheets, will become damaged or deformed. Moreover, this heat also affects the mode of functioning of adjoining machine elements, if these are heated above the permissible level.
Additional cooling devices are known, the purpose of which is to prevent overheating of printing press elements in the region of the dryer. To cool sheet-guiding surfaces in the region of action of dryers, channels for cooling agents are disposed on the underside of dryers (for example, DE 19810387 C1) However, the cooling effect is limited to the baffle plate but the adjoining cylinder groups and printing stock are not cooled.
The use of a refrigerated air blast for cooling cylinders is known, for example, from DE 4326835 A1 and DE 4307732 A1, which show additional air blast cooling beams with cycled cooling air for cooling rubber and/or plate cylinders limited to the blowing device. The portion of the cooling air, flowing back from the cylinders surface, is exhausted once again at the air blast cooling beam, cooled again and then, once more, blown onto the upper surface of the cylinders. Moreover, DE 43 07 732 A1 discloses a temperature-controlling system for three adjacent cylinders, which has an outer air-circulation cycle, for which leakage air of the air blast cooling beams is returned to the cooling device from the closed airspace formed by the adjacent cylinders, the air blast cooling beams and additional boundary surfaces.
Furthermore, WO 01/32423 A1 discloses the cooling of printing stock heated by dryers, as well as indirect cooling of printing cylinders and transfer cylinders by air blast cooling devices, which have cooling registers and ventilating fans and are additionally disposed before the printing zone. This air blast cools the printing cylinders on the sheet-guiding casing section. As a result, there is intensive cooling of the printing stock. However, because of the insulating effect of the sheet on the cylinder, cooling of the cylinder is not satisfactory. Furthermore, the relationship between the intensity of the cylinder cooling and the nature of the printing stock is a disadvantage.
For cooling sheet-shaped printing stock, especially sheets, which are in danger of being distorted, additional cooling air-blowing facilities are provided below the transfer cylinders and/or ahead of the printing zone according to DE 10158050 A1 and DE 10158051 A1. Such facilities can be integrated partly into existing sheet-guiding facilities.
The object of DE 101 52 593 A1 overcomes the disadvantage of the need for additional space for the cooling devices by arranging cooling registers in the air stream of existing air blast sheet guiding devices below the transfer cylinders, in front of printing columns and above transfer regions in the UV dryer area.
All of the cooling systems mentioned above have the common disadvantage that they are designed only for special cooling tasks, that is, either only for cooling printing stock or only for cooling cylinders and have only strictly limited areas of effectiveness. However, especially when printing temperature-sensitive plastic sheets, it is important to cool not only the printing stock intensively but also the machine elements guiding the printing stock.